1. Field of the Invention
The present invention relates to a pattern-printed transparent sheet which is a member capable of being applied to a data input system of a type of handwriting directly on a screen of a display device and providing a coordinate detect means and which has particularly a broad read angle.
2. Related Art
In recent years, increased is necessity to convert handwritten characters, pictures and the like to electronic data which can be handled by information processing devices. In order to meet the above situations, it is considered to combine matters on which patterns reflecting an infrared ray and a UV ray being non-visible lights are printed as a position information for showing positions of input lines.
On the other hand, a device in which a position information are read by a pen type sensor and the like and input into an image display device of an information liquid crystalline high polymers disclosed in Japanese Patent Application Laid-Open No. 293252/1999 can be used as the liquid crystal polymers described above.
The chiral agent contained in the transparent ink used in the present invention is a material which has an asymmetric carbon atom and which forms a chiral nematic phase by mixing with a nematic liquid crystal, and it shall not specifically be restricted as long as it has a polymerizability. A material having an acrylate structure represented by Formula (12) is preferred since it is polymerizable by irradiation with a UV ray.
X is 2 to 5 (integer).
The property of reflecting an infrared ray by the transparent pattern in the present invention makes preferably use of, as described above, a wavelength selective reflectivity (the same principle as Bragg reflection in X-ray diffraction) of a liquid crystal material having a cholesteric structure. The selective reflection peak wavelength thereof (wavelength satisfying the Bragg reflection conditions) is determined by a pitch length of a cholesteric structure processing instrument includes, for example, a sheet disclosed in a patent document 1, which is a transparent sheet mounted on a front face of a display device and on which marks capable of providing a position information for showing the positions of input lines by an electronic pen for input and the like are printed by using an ink emitting light capable of being read by the above input line read means by irradiating with light having a prescribed wavelength.
Further, a coordinate input device prepared by using a transparent member on which a specific ink reflecting light in an infrared region is printed is disclosed in a patent document 2.
However, it is the existing situation that the examples of the specific transparent sheets are not shown in the patent documents 1 and 2 and that only an idea or a desire of the transparent sheets is described therein.
Accordingly, the present inventors have used a cross-linked and fixed cholesteric liquid crystal as a print ink for lattice points for inputting a coordinate to set a selective reflection wavelength of the above cholesteric liquid crystal layer to an infrared region, whereby they have invented a coordinate input sheet which is transparent to a visible light and in which lines drawn by a pen can be input by an infrared ray, and patents thereof have been applied (Japanese Patent Application No. 150121/2006 and Japanese Patent Application No. 269220/2006). However, further intensive investigations repeated by the present inventors have resulted in finding a new problem; in general, an orientation layer for orienting a liquid crystal is present in a lower layer of a cholesteric liquid crystal layer, and the orientation layer is subjected to orientational treatment such as rubbing treatment, whereby the cholesteric liquid crystal is oriented in a line while drawing fine spirals so that a helical axis is vertical to a plane surface of a substrate; in this regard, if the helical axis stays in a line vertically all over the plain surface of the substrate (that is, the respective film surfaces of a multilayer film structure are parallel plain surface groups), such a kind of a pen as used for reading can detect only a retroreflective component, and therefore only the component in a 0° (vertical) direction is read; and thus, it has been found that if the input pen inclines a little, a sensitivity of detection is dramatically reduced.
Accordingly, a read angle is required to be expanded in order to enhance a precision of detecting and reading a coordinate point.
On the other hand, a reflection type color filter structure for a liquid crystal display device which reproduces colors by reflection is disclosed in, for example, a patent document 3 as a conventional technique regarding a cholesteric liquid crystal pattern which reflects a non-visible light. In the above case, a reflection type filter structure comprising a first region reflecting a red light toward a vertical direction and further a second region reflecting an infrared ray (non-visible light) toward a vertical direction is disclosed as means for enhancing only a reflectance of a red light in an oblique direction without enhancing a reflectance of a red light in a vertical direction more than necessary in a red light reflection color filter. In the structure described above, the above second region is not increased in a reflectance of a red light in a vertical direction by reflecting an infrared ray toward a vertical direction. In addition thereto, a selective reflection wavelength of light incident to an oblique direction is shortened (refer to an equation described later), and therefore a red light in an obliquely incident light is reflected. Thus, the pertinent object is achieved. Further, diffraction gratings, circularly polarized plates, optical filters, colored decoration materials and the like each prepared by using a liquid crystalline film in which a cholesteric liquid crystal layer or a chiral smectic C liquid crystal layer is formed on a whole surface are disclosed in patent documents 4 and 5. In the above case, it is disclosed that in the multilayer membrane structure of the above cholesteric liquid crystal layer, curving or folding the above membrane from a parallel plane face provides the effects of reducing a dependency of a viewing angle in coloring and imparting a polarizing property to a diffraction light and that reducing specular reflection of an outside light provides the effect of reducing a viewing angle dependency.
In all the above cases, however, neither uses for coordinate input are desired nor it is indicated therein to form a cholesteric liquid crystal layer in a pattern shape in the uses for coordinate input.    Patent document 1: Japanese Patent Application Laid-Open No. 256137/2003    Patent document 2: Japanese Patent Application Laid-Open No. 243006/2001    Patent document 3: Japanese Patent Application Laid-Open (through PCT) No. 519728/2004    Patent document 4: International Patent Publication WO99/034242 pamphlet    Patent document 5: Japanese Patent Application Laid-Open No. 154865/2006